This invention generally relates to transmission of electromagnetic waves between two regions divided by a solid window penetrable by the electromagnetic waves. The electromagnetic properties of the window are generally different from the properties of the matter that makes contact with the windows. The general purpose is to transmit through the window the maximum amount of energy carried by the electromagnetic waves, i.e., to minimize the dispersion, reflection, and dissipation, at the same time maintaining the structural integrity of the window.
More specifically, a microwave-based evaporator/vaporizer has a waveguide coupled to a high-pressure vessel. A docking collar safety device is positioned between the waveguide and the high-pressure vessel. The evaporator/vaporizer system vaporizes liquefied compressed gases such as ammonia (or other similar liquid) at high flow rates. The gases are usually under moderate to high pressure and can be toxic or hazardous if exposed to the atmosphere. The microwave evaporator for an ammonia application typically operates at 114 psig.
The docking collar or a safety device must efficiently pass microwaves into the vessel and provide a pressure barrier to prevent high pressure and toxic gases from escaping from the vessel in undesired ways. The following prior art apparatuses use double window assemblies specially designed for their application. None imply or suggest the present invention.
European Patent 0,614,575 B1 and U.S. Pat. No. 5,200,722 disclose a dual window assembly adapted to uniformly transmit high power microwave energy from a source, such as a waveguide, at atmospheric pressure into the interior of a vacuum deposition etch chamber. Cooling fluid passes inside the narrow gap between the two windows to reduce the temperature of the windows positioned in the wall of the vacuum chamber to allow high power microwaves to pass without producing thermal failure of windows even over extended periods of time.
European Patent 0,505,066 B1 and U.S. Pat. No. 5,175,523 pertain to vacuum-sealed dual dielectric windows for transmitting electromagnetic waves between sections of a waveguide containing different atmospheres, such as a high-vacuum electron tube (such as a klystron or a gyrotron) and a pressurized waveguide. Each window is a plate of thickness equal to about one half of a wavelength in the dielectric-filled guide transmitting transverse electric wave TE011, so that the reflections at the two faces add out of phase and cancel at the center frequency. The two windows are displaced by one-quarter wavelength of the evacuated or coolant-filled guide giving a similar cancellation. The window assembly comprises two parallel dielectric plates, spaced apart, with coolant flow confined between them. Since high coolant flow and pressure is needed at very high microwave power levels, the dielectric plates (windows) are required to be as thin as possible at high frequency. On the other hand, the existing stresses can cause failures of the dielectric plates. Applying an inward force between the plates reduces the stress in the dielectric plates by a coaxial structure at the axial center of the plates where the electromagnetic field is low.
European Patent 0,343,594 B1 and U.S. Pat. No. 4,965,541 relate to an improved waveguide provided with double disk window assembly having microwave-transmitting dielectric disks. The disks are spaced as close as possible to each other. A coolant flows in the gap between the dielectric disks cooling the disk window assembly. A waveguide employs this transmission window, for example, in the output section of a microwave electron tube (such as a klystron, a traveling wave tube, and a gyrotron or microwave transmission line of a particle accelerator). To increase the operating frequency of the waveguide, the double-faced disk cooled window assembly of that waveguide has to employ thin dielectric disks for wide pass band performance. If the thickness of the dielectric disks is increased, the pass band of the microwaves will be narrow.
U.S. Pat. No. 4,286,240 pertains to high power microwave transmission and discloses an apparatus for conducting very high microwave power at very high frequencies. A circular waveguide transmitting a circular electric field mode is used. The vacuum-tight window of an electron tube is often the element with the lowest power-handling capability. The patent discloses a window that has two dielectric plates with a space between them. There is a gap in the waveguide inner wall through which a dielectric fluid is circulated between plates to cool them. The gap leads to a region containing wave-absorbing material, such as water, to absorb modes other than the circular electric-field mode.
U.S. Pat. No. 5,455,085 relates to a window for coupling electromagnetic energy through a wall and between two waveguides, particularly between two environments such as a high-pressure environment and a low-pressure environment. The window has two panes spaced apart by a quarter wavelength for inhibiting reflection and a construction permitting easy disassembly for replacement of components for adapting the window to different frequencies of radiation. The window is suitable for use in satellite communications wherein alignment and test of satellite electronics is to occur in a laboratory on earth while the satellite electronics may be mounted within a vacuum chamber to simulate the environment of outer space.
Accordingly, to date there exists a need for a docking collar/safety device that:
1. Efficiently transmits up to 30 kW of microwave power ranging from 915 MHz to 18000 MHz via a waveguide system into an evaporator vessel containing liquefied compressed gases, such as ammonia.
2. Provides an adequate pressure barrier to block the vaporized gas under high pressure from escaping into the waveguide system or immediate environment.
3. Has an optimized design minimizing heat loss dissipation.
4. Alerts an operator if a pressure breach at the interface of the waveguide and vessel occurs and allows a controlled shutdown of the microwave-based evaporation system.